Adds find and all methods to mamba.model.Model.

    * Add find method that can be used with or without a class instance:
        customer = yield Customer.find(name=u'John')
        customer = yield Customer().find(name=u'John')
        customer = yield Customer.find(Customer.name == u'john')
    * Add 'async' magic named boolean argument to Transactor.run so we can now run a @transact decorated method synchronous just as:
        customer = Customer.find(name=u'Pam', async=False)
        customer = Customer().read(1, async=False)
    * Added several unit tests
    * Fixes some model tests that weren't working